The invention relates generally to arthroscopes, endoscopes and similar optical instruments and more specifically to variable view arthroscopes.
Arthroscopes and similaroptical instruments, such as endoscopes, are used in medical applications, such as suirgery and examination, as well as in non-medical applications that similarly involve visual inspection of a confined or inaccessible space that constitutes the working area. Although the present invention is described here with reference to an arthroscope or similar instrument employed for surgery, the invention may be useful for other applications and is intended to embrace all suitable variations.
Over the last fifteen or more years, minimally invasive surgery has become a mainstream surgical technique. Within the orthopedic field, in particular, arthroscopy and similar techniques that employ devices such as arthroscopes have become the most common surgical procedures. Minimally invasive surgery is less painful for the patient and, in most instances, can be performed more quickly and safely than surgery that requires greater invasion of the patient""s body; other benefits of minimally invasive surgery include that administration of anesthesia is simpler for minimally invasive surgery, that patients heal more quickly, that hospital stays may be reduced in length or even eliminated, and that the procedures are more cost effective.
The value of using minimally invasive surgical techniques may be limited by the capabilities of the arthroscopes, endoscopes and other principal optical instruments employed. In particular, the rather limited field of view afforded by even the best available instruments that satisfy the dimensional and other requirement of surgical applications has limited the useful scope of minimally invasive surgical techniques. Typically, the larger the field of view, the greater the usefulness of the instrument for most applications.
Several methods for widening the field of view offered by arthroscopic/endoscopic instruments have been proposed, but they have not been especially successful. Generally, such proposals have required packing a plurality of movable lenses or prisms into the input end of the instrument; the resulting problems of precision of construction, precision of relative movements, space requirements, optical distortions, and elimination of undesired ambient light have been substantial.
Illuminating the viewing area to obtain a usable image is another requirement of arthroscopes and similar instruments. Without adequate light, the resultant image does not contain sufficient information to be maximally useful. Light is typically provided to the object input end of the arthroscope from an external source through a light guide. The light from the external source is transferred to an internal light guide in the arthroscope at one end of the arthroscope and transmitted to the distal end of the arthroscope via the internal light guide, where the light generally diffuses to light the viewing area around the distal end of the arthroscope. The external source typically includes a light connected to a fiber optic bundle; the external fiber optic bundle is mechanically coupled to the internal light guide, which is typically also a fiber optic bundle. Typically, the external source and the internal optical fiber light guide are standard parts that are commercially available. The coupling efficiency, that is, the amount of light that actually passes from the light source to the viewing area, is relatively poor.
The poor coupling efficiency results in part from the difficulty in controlling the light emitted from the external source fiber optic bundle and focusing that light into the internal light guide and in part from the physical structure of a bundle of optical fibers. Matching the numerical aperture and spot size of the external source in the receiving internal light guide is very important for coupling efficiency. The numerical aperture of an optical fiber is a mathematical representation (the sine of the half angle of the full cone of light that can be accepted by the optical fiber and completely transmitted without any loss) of the angle at which light may strike the surface of an optical fiber that is perpendicular to the optical axis of the fiber and still travel down the fiber. Light that strikes that surface at too great an angle as measured from the optical axis of the fiber, i.e. exceeds the numerical aperture of the fiber, will be lost. The spot size of a light beam is defined by the circular area within which a large percentage of the light is contained at a particular distance from the source of the light beam. The most efficient light transfer occurs when the transmitted light falls within the numerical aperture of the receiving fibers and the spot size of the transmitted light is smaller than the core of the receiving fiber. A focusing lens or focusing system may be used to aid in directing the light from the source appropriately. Typically, if the spot size of the external light source is reduced by a focusing lens, then the cone angle of the converging light from the focusing lens may exceed the numerical aperture of the receiving fiber, and the light that exceeds the numerical aperture of the receiving fiber will be lost. Conversely, if the cone angle of the converging light is less than the numerical aperture of the receiving fiber, then the spot size of the converging light may be larger than the core size of the receiving fiber, and the light that exceeds the core size of the receiving fiber will be lost. Matching the numerical aperture and spot size of the source fiber to those of a receiving fiber, such as between the external light source and the internal light guide, can be especially difficult when the source is a bundle of fibers. Also, when attempting to focus light from a bundle of fibers into a second bundle of fibers, the coupling efficiency is greatly reduced because a single focusing system is attempting to focus a group of spots simultaneously. Since only one ray is actually on the focusing system optical centerline, all other rays from the source fibers, as they spread out from the center of each fiber, are decentered and unsymmetrical in the focusing lens. They therefore cannot match both the spot size and numerical aperture of the receiving fibers. The greatest coupling efficiency is achieved through a compromise between the spot size and the cone angle of the converging light, i.e., when the converging light most nearly matches the core size and numerical aperture of the receiving fiber and when the optical centerlines of the emitting fiber, the focusing system, and the receiving fiber are coaxial.
An additional problem that leads to poor light transmission to the viewing area results from the construction of bundles of fibers. A single optical fiber consists of a core (the light carrying portion) and the cladding (the covering of the core that causes the light to stay contained within the core). Only the cores of the bundled fibers carry light; therefore, light is lost due to the spaces between the cores. When a group of fibers having circular cross-sections is bundled into a cylindrical configuration, only about 78% of the cross-sectional area of the cylindrical configuration is taken up by fibers. Also, the core of each of the bundled fibers is smaller than the cladding. Consequently, the actual light-carrying area is significantly smaller than the circular cross-section of the bundle. Improved light transmission to the distal end of the arthroscope will improve the illumination of the viewing area and increase the information contained in captured images.
There is a need for an arthroscope that affords a wide effective field of view and that does not require movement of the arthroscope to vary its scope of view. One such arthroscope is disclosed in copending U.S. application Ser. No. 09/243,845, entitled xe2x80x9cVariable View Arthroscope;xe2x80x9d which has a common inventor with the present application. Another such arthroscope is disclosed in copending U.S. application Ser. No. 09/452,340, entitled xe2x80x9cVariable View Arthroscope;xe2x80x9d which also has a common inventor with the present application. The referenced applications are incorporated herein by this reference. There is also a need for an improved light relay system for illuminating the viewing area through an arthroscope. In this specification and in the appended claims the term xe2x80x9carthroscopdxe2x80x9d means and should be interpreted to include an endoscope or any other similar optical instrument, whether used for surgery or otherwise.
A variable view arthroscope in accordance with the present invention includes a variable object input assembly in an elongated housing tube, a control to vary the view of the object input assembly, and a lighting assembly to illuminate the viewing area. An input window, located in the input end of the housing tube, allows a view of the working area. The input window is preferably spherical. The object input assembly includes an input lens, a first mirror, and a second mirror. The input lens is movable and the first mirror is rotatable. The input lens and the first mirror move around the same axle. The second mirror is fixed. The reflected light from the viewing area forms a working image and the light image or object rays pass from the viewing area through the input window and the input lens, reflect from the first mirror to the second mirror, and reflect from the second mirror into a relay lens system. In some embodiments, the second mirror may be replaced by a prism.
The control varies the position of the input lens and first mirror to any position, or to a series of fixed positions, between a first limit position and a second limit position. As object rays pass through the input lens to the first mirror, to the second mirror or prism, and into the relay lens system, the length of the axial ray remains the same when the angle of view of the arthroscope changes. Also, the lengths of the rim rays may be equal to each other and may also remain the same when the angle of view of the arthroscope changes.
In another aspect of the invention, the lighting assembly preferably includes a relay light guide formed from one or more rods of transparent material with mirrored surfaces. The relay light guide preferably captures each light ray from an external source and transmits the ray to the viewing area.